A polybutadiene has a bonded portion generated through polymerization at 1,4-site (1,4-structure) and a bonded portion generated through polymerization at 1,2-site (1,2-structure) of butadiene, which are so-called microstructures and coexist in a molecular chain. The 1,4-structure can be further classified into two types: a cis-structure and a trans-structure. On the other hand, the 1,2-structure is structured to have a vinyl group in a side chain.
As known, polybutadienes different in the above microstructures can be produced depending on polymerization catalysts and polymerization conditions and have been employed for various uses in accordance with the properties thereof.
For the purpose of improving the abrasion resistance and heat built-up property of tires, blending a polybutadiene rubber (BR) in natural rubber or the like has been widely implemented and examples of the BR have been proposed variously. For example, JP 7-118443A (Patent Document 1) discloses a BR having a weight average molecular weight of 500,000-750,000, a molecular weight distribution of 1.5-3.0, and an intrinsic viscosity of 90 or more. JP 2001-247721A (Patent Document 2) discloses a BR having a cis-content of 95% or more, and a molecular weight distribution of 3.5-6.0. JP 2004-339467A (Patent Document 3) discloses a BR having a cis-content of 95% or more, a mooneey viscosity (ML) of 30-42, a ratio of a 5% toluene solution viscosity to ML of 1.8-5.0, and a molecular weight distribution of 2.5-3.8.
For the purpose of improving the abrasion resistance and flex cracking resistance of tires, JP2004-339466A (Patent Document 4) discloses a BR having a cis-content of 95% or more, a ML viscosity of 50-70, a ratio of a 5% toluene solution viscosity to ML of 1.8-5.0, and a molecular weight distribution of 1.8-3.8.
The BR for use in tires has a problem because an increased molecular weight improves the abrasion resistance while it deteriorates the processability. In contrast, a widened molecular weight distribution improves the processability while it deteriorates the abrasion resistance and rebound. Thus, there is a need for improving the processability and abrasion resistance.
Patent Document 1: JP 7-118443A
Patent Document 2: JP 2001-247721A
Patent Document 3: JP 2004-339467A
Patent Document 4: JP 2004-339466A